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What is TWC System low efficiency bank 1 mean?

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Posted on Jan 02, 2017

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SOURCE: 1998 grand am 2.4 liter, engine code po420 (twc

What this means is that the three way catalytic converter is not doing it`s job and it needs to be replaced.First check the exhaust system and make sure it is not bent or has holes.If it`s good then make sure the rear o2 sensor is working properly.If that`s good the you will have to replace the cat.converter.Good luck.

Posted on Dec 06, 2009

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What does a ******** Catalyst(TWC) system, low efficency service code mean? and where is it located

Exhaust Converter on Bank #1 side, is worn out,needs
to be replaced

PO420 &PO430 are Converters Below Efficiency

Should have lasted another year or two

I suspect you don't keep up on what the car
required,air filter,spark plugs,O2 Sensors & the like.

Your fuel trim & ignition issues over the years ruined it

Jun 02, 2012 | 2001 Cadillac Seville

2 Answers

I have a dodge ram 2500 5.9 cummins showing a code of p0140. What's this code

From this website:

P0140 - 02 Sensor Circuit No Activity Detected (Bank 1 Sensor 2)

What does that mean?

The Powertrain control module (PCM) will provide a .45 volt reference voltage to the Oxygen sensor. When the O2 sensor reaches operating temperature, it will generate a voltage that will vary depending on the oxygen content of the exhaust. Lean exhaust generates a low voltage (less than .45V) and rich exhaust generates a high voltage (greater than .45V). O2 sensors on a specific bank marked as "sensor 2" (as this one is) are used to monitor emissions. A Three-Way Catalyst (TWC) system (catalytic converter) is used to control tailpipe emissions. The PCM uses the signal received from Oxygen sensor 2 (#2 indicates aft of catalytic converter, #1 indicates pre-converter) to read efficiency of TWC. Normally this sensor will switch between high and low voltage at a noticeably slower rate than the front sensor. This is normal. If the signal received from rear (#2) O2 sensor indicates that the voltage has "stuck" between .425V to .474 V, the PCM determines this sensor is inactive and this code will set.

Potential Symptoms

Your check engine light(CEL), or malfuction indicator lamp (MIL) will be illuminated. There will not likely be any noticeable drivability problems other than the MIL. The reason is this: The rear or post catalytic converter Oxygen sensor does not affect fuel deliver(this is an exception on Chryslers). It only MONITORS the efficiency of the catalytic converter. For this reason, you will likely not notice any engine trouble.


The causes for a P0140 code are fairly few. They could be any of the following:

Shorted heater circuit in O2 sensor. (Usually requires replacement of heater circuit fuse in fuse block also)

Shorted signal circuit in O2 sensor

Melting of harness connector or wiring due to contact with exhaust system

Water intrusion in harness connector or PCM connector


Possible Solutions

This is a fairly specific problem and shouldn't be too difficult to diagnose.

First, start engine and warm up. Using a scan tool, watch the Bank 1, sensor 2, o2 sensor voltage. Normally the voltage should switch slowly above and below .45 volts. If it does, the problem is likely intermittent. You'll have to wait for the problem to surface before you can accurately diagnose.

However, if it doesn

Apr 15, 2011 | Dodge Pickup Cars & Trucks

3 Answers

Diagnostic trouble codes dtc po420 po102


Jan 26, 2011 | 1997 GMC Jimmy

1 Answer

1997 mercury sable po 420 bank 1 which sensor do i change.

That could be the cataylic convetor you could try the oxygen sensor behind the cat the last one to the rear of the vehicle bank 1 sensor # 3 but P0420 is TWC system witch means low efficiency in the cat but it could be a sympthom of an other problem but if the code is 0420 thats where i would start

Nov 17, 2010 | Mercury Sable Cars & Trucks

1 Answer

My engine light came on. i had an OBD2 scan done and the code P0430 popped up. it's nthe catalyst system low efficiency bank 2. on the way home tonight my truck started shaking and vibrating a little at...

The low efficiency bank 2 means that the material inside the catalytic converter is deteriorating and needs to be replaced. FYI. Bank 2 refers to the side of the motor with cylinder number 2 on it.

Sep 27, 2010 | 1998 Chevrolet K1500

2 Answers

P0420 code on my 2003 chevy s10

please go to the provide link for diagnosis of this code,but the bottom line here is the catalytic converter may be worn out

Aug 06, 2010 | 2003 Chevrolet S-10

2 Answers

1998 grand am 2.4 liter, engine code po420 (twc system low efficiencty bank 1) what does this code mean

Catalyst System Efficiency Below Threshold Bank 1
this is code P0420.
It's telling you converter is not as efficient as it should be.You can drive it like this forever,or spend to replace a converter.

Dec 06, 2009 | 1998 Pontiac Grand Am

1 Answer

Vsc and check engine light is on . Had it read and code p0420 came up. Autozone said it could be an air leak in exhaust, AF sensor error, fuel system fault or faulty catalytic converter. Is there a cheap...

DTC P0420: Catalyst System Efficiency Below Threashold (Bank 1)

The ECM uses sensors mounted before and after the three-way catalyst (TWC) to monitor its efficiency. The first sensor, and Air Fuel ratio (A/F) sensor, sends pre-catalyst A/F ratio information to the ECM. The second sensor, a heated oxygen sensor (O2S), sends post-catalyst information to the ECM. The ECM compares these two signals to judge the efficiency of the catalyst and the catalyst's ability to store oxygen. During normal operation, the TWC stores and releases oxygen as needed. The capacity to store oxygen results in a low variation in the post-TWC exhaust stream as shown below.
If the catalyst is functioning normally, the waveform of the heated oxygen sensor slowly switches between RICH and LEAN. If the catalyst is deteriorated, the waveform will alternate frequently between RICH and LEAN. As the catalyst efficiency degrades, its ability to store oxygen is reduced and the catalyst output becomes more variable. When running the monitor, the ECM compares sensor 1 signals (A/F sensor) over a specific amount of time to determine catalyst efficiency. The ECM begins by calculating the signal length for both sensors (for the rear oxygen sensor, the ECM uses the output voltage signal length). If the oxygen sensor output voltage signal length is greater than the threshold (threshold is calculated based on the A/F sensor signal length), the ECM concludes that the catalyst is malfunctioning. The ECM will turn on the MIL and a DTC will be set.
Hope this helps :)

Oct 19, 2009 | 2005 Toyota Highlander

2 Answers

Po420 twc system low bank 1 code

Vehicle needs a Primary or first position Oxygen sensor, bank one just means it's the O2 sensor before catalytic converter

Jul 02, 2009 | 1999 GMC Yukon

1 Answer

PO420" Catalyst efficiency low Bank 1"

Replace the catalytic converter.

Mar 09, 2009 | 1999 Acura TL

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